#include <iostream>

using namespace std;
/* run this program using the console pauser or add your own getch, system("pause") or input loop */

int main(void) {
	int n;
	int sum;
	while(cin>>n)
	{
		sum=0;
		for(int i=1;i<=n;i++)
		{
			sum=sum+i;
		}
		cout << sum << endl <<endl;
	}
	
	return 0;
}
